1. Field of the Invention
The invention relates to an electronic device, and more particularly, to a thin film transistor.
2. Description of Related Art
With the development of the technology, minimization of electronic devices has become the trend. The present structure of the conventional metal-oxide thin film transistor (MO-TFT) is a bottom-gate-etching-stop structure. In the above structure, a source and a drain are located in the same layer and are respectively disposed on both sides of the semiconductor layer. An etching stop layer has two contact holes which expose a top surface of the semiconductor layer. The source and the drain respectively fill the two contact holes and are thus electrically connected to the semiconductor layer. However, the setting of the two contact holes is not conducive to reducing the size of TFT, and thus unable to meet the requirements of high resolution and narrow border of the display panels.
In order to meet the above requirements, a TFT in which a contact structure between a source and a semiconductor layer is different from a contact structure between a drain and the semiconductor layer has been developed. In this TFT structure, the source is covered with the semiconductor layer, and the drain is electrically connected to the semiconductor layer through the contact hole. However, different contact resistances may be formed in the different contact structures at the junction between metal and semiconductor above. Accordingly, the development of a TFT can meet the excellent electrical stability and the small size is necessary.